1. Field of the Invention
The disclosure relates generally to a developing roller for an electrophotographic image forming apparatus, and a manufacturing method of the same, and more specifically, to a developing roller that ensures an increased toner charging amount and a uniform optical density.
2. Description of the Related Art
An electrophotographic image forming apparatus, such as a laser printer, a facsimile, or a copier, generally employs an image forming configuration in which one or more of a charging roller, a developing roller and a transfer roller are arranged around a photosensitive medium. In an electrophotographic image forming apparatus of such configuration, a developing agent such as, for example, toner, is supplied from a developing device to the photosensitive medium during the image forming operation.
By way of example, during an image forming operation, the surface of the photosensitive medium is charged by the charging roller to a uniform electrical potential, and is then exposed to light from a light exposure unit discharging selective portions of the surface to causes an electrostatic latent image as a pattern of potential difference corresponding to the desired image to be formed on the surface of the charged photosensitive medium. The developing roller supplies the developing agent to the photosensitive medium to thereby visualize or develop the electrostatic latent image into a developer image. The developer image is then transferred by the transfer roller onto a printing medium such as, for example, a sheet of paper, as the printing medium passes between the photosensitive medium and the transfer roller.
The developing roller of such electrophotographic image forming apparatus needs to have suitable transfer characteristics and resiliency so as to reliably contact the photosensitive medium, and to transfer toner onto the electrostatic latent image. Although a non-magnetic mono-component developer is widely used in the image developing art, due to the difficulty in controlling the charging of the toner, the toner being carried on the developing roller may be inconsistently or unstably charged, resulting in image defects such as, for example, ghosting. It is particularly difficult to obtain high quality images with high optical density under lower temperature and/or in low humidity environments. There thus remains a need in the art for improvement in the developing rollers for use in an electrophotographic image forming apparatus.